const mapi.MDB_NO_DIALOG;

Prevents the display of logon dialog boxes. If this flag is set, and OpenMsgStore does not have enough configuration information to open the message store without the user's help, it returns MAPI_E_LOGON_FAILED. If this flag is not set, the message store provider can prompt the user to correct a name or password, to insert a disk, or to perform other actions necessary to establish connection to the message store.